The cheap mStar-based tuners/DVRs (iView, HomeWorx, ViewTV, etc.) all let you manually scan TV channels one frequency at a time. So does the old (but still good) DTVPal DVR (aka the CM-7000Pal). You can also do a full auto-scan, then delete unwanted channels, to get a quick start. However the program guides on all these devices come from broadcast PSIP data only.
A Channel Master DVR+ (CM-7500) will also let you manually scan channels, and has an Internet-based guide that goes off your Zip code and the display channel numbers, so it doesn't care about the actual frequency. Its only weakness (with current firmware) is the inability to delete unwanted channels if you do a full auto-scan; you can only "hide" them.
All of these are worth looking at if you're dealing with translator stations or equipment that changes the RF frequency of digital channels. But none let you attach your "own" guide data to a channel. For that you need PC-based PVR software. I know Windows Media Center will do it, if you can find a copy of Windows that came with it. You'd have to decline the Microsoft-based guide and provide your own via an .xmltv file.